Process of tanning.



- No Drawing. I

v UNITED STATES PATENT OFFICE.

, JOSEPH GUSTAVE S'IODOLA, OI AGRAM, AUSTRIA-HUNGARY, ASSIGNOR TO GUSTAV J. A. TROSTEL, OF MILWAUKEE, WISCONSIN.

PROCESS OF TANNING.

'0 all whom it may concern:

Be it known that I, JOS PH GUSTAVL S'ronoLA, a subject'of the Emperor of Austria-Hungary, residing at Agram, in the Province of Croatia and Empire of Austria- Hungary, have invented a certain new and useful Process of Tanning, of which the following is a specification.

My invention or discovery provides a new and useful process for tanning hides and skins by the use of iron and chromium compounds-to produce durable leather. By the expression durable leather I mean leather which is so tanned that-the action of water does not wash out the tanning agent or agents, as distinguished from such leathers as the alum tanned leathers.

Chrome tanning methods are well known in the art, and are extensively used in the production of leathers, but these methods are expensive not only on account of the comparatively high cost of the chromium salts employed, but also because the leather produced by these methods has a peculiar greenish or bluish hue which must be concealed or disguised by dyes before the leather is acceptable to users.

Iron salts are cheap, and as they possess the property of tanning'hides and skins, they -would make most desirable tanning agents,

but' unfortunately they produce a harsh leather which is not generally suitable for the uses to which leather is applied. I have discovered however, that the salts of iron and chromium can be used together in such a manner in tanning hides and skins, that the resulting leather is as good and serviceable as chrome or vegetable tanned leather,

and has a nice yellow or buff color, so that it is acceptable to users without previous dyeing. By my discovery therefore,l am enabled to produce marketable leather at a lower cost for tanning agents than heretofore, and which requires no expense for dyes.

In this specification and the claims, the term hides is used generically to include all classes of hides, skins and pelts.

In tanning hides by my new and improved Specification of Letters Patent,

Patented Jamil, 1916.

Application filed Karch 12, 1909. Serial No. 482,920.

process,'it is possible to vary the steps of the process somewhat, and. it is possible to ployed somewhat, and the steps of the process and the proportions of materials should be altered as required by existing conditions at different tanneries, these matters being matters which the judgment and skill of the tanner must'determine. IVithout therefore, specifically limiting my process to the exact succession of steps which I am about to describe, and to the exact proportions of materials which. I am about to sta'te, I describe now at length what I consider at the present time to be the most preferable process for using iron and chromium compounds in tanning leathers, and this description gives in exact sequence and in exact proportions, full and explicit instructions for tanning hides according to my new process, without however depriving me of theright to make variations therein as required by special circumstances, or as may seem advisable under certain conditions.

The hides are treated in the usual preliminary ways known to all tanners, to accomplish the removal of salt, dirt, hair, etc.,

as though they were to be tanned by any of the well known processes. They'ar'e also bated in the usual manner, and are then treated as follows; it being understood that the weight of hide to be tanned determines the proportions of the agents specifically given -for a certain weight of hides, and it .should also be understood that when solu- .50 vary the proportions of the materials emof 66 Baum scale, and 30parts of common salt. Preferably the white bated hides are placed in a drum together with this pickling solution, and drummed for one hour; then they are allowed to rest in this pickling solu tion for a further period of twelve hours. As the result of this pickling process the hides should absorb approximately one per cent. (calculated on the weight of the bated hides, or what is known to tanners as the white wei ht, so that the total weight of the bated %iides and absorbed acid will be approximately 101 per cent. of the weight of the bated hides) of acid, calculated as sulfuric acid; that is to say, the one percent. of acid though consisting of sulfuric acid and muriatic acid, is calculated as though it were all one acid. Thereafter, as the preferable form of treatment, there is added to' the pickled hides, a one-bath chrome liquor such as is ordinarily used in makingchrome tanned leathers, such as, for example, the

liquor of the Dennis Patent No. 495,028 of April 11, 1893, or any similar and equivalent liquor. The purpose of this is to give the white-hides a. preliminary chrome tannage.

This preliminary chrome tannage l at present consider as the best method of proceeding in carrying out my process. Where the chrome is added at this stage of the process, the amount of the one-bath chrome liquor to add depends on the kind of leather it is wished to-produce, as when the quantity of chrome liquor is increased, the resulting leather is softer, and vice versa, so the tannercan easily govern this in accordance with the results desired.

While I have stated the use of a one-bath chrome liquor for giving a preliminary chrome tannage, it is not to be understood that this preliminary chrome tannage by the one-bath chrome liquor excludes a preliminary chrome tannage by the ordinarytwo-bath chrome process, as one method is the equivalent of the other as far as my new and improved process of tanning is concerned. Where however, the preliminary chrome tannage is given by the two-bath process, the hides or leather should first be washed before proc-eding with the subsequent steps of the process. In some two bath chrome processes there is a large precipitation of sulfur and this sulfur would act detrimentally on the subsequent iron and chrome solution and the object of the washing is to get rid of the sulfur as much as possible, but where the one-bath chrome process is used, there is no sulfur and no washing is required.

lln'describing my process I am following what seems to me to be the simplest way of explaining it so that it will be readily understood. As described heretofore, the white, bated hides are placed in a tanning somer drum, for convenience of treatment, with the pickling solution. The one-bath chrome liquor is added to the drum containing the hides and the residual pickling. solution. The hides and these solutions constitute the contents of the drum when the stock iron and chrome solution described in-the next paragraph is added to-the contents of the drum. If, however, the hides have been removed from the drum and washed as describedin connection with the preliminary tannageby some two-bath chrome processes, then the hides are put into the drum with water before the stock iron and chrome solution is added to the contents of the drum.

The hides are then drummed in atanning drum or treated by equivalent mechanism for a few hours, .and then there is added to the contents'of the drum, 34 parts 'of a stock iron and chrome solution which is hereinafter described, and the hides are then drummed for several hours. The partially tanned hides are allowed to remain in this liquor over night or, for an e'qulvalent period of time, and'the first thing in the morning there is again added a further quantity of the stock iron and chrome so- 7 lution' whichhas first'been treated in the following mariner 30 parts of the stock iroh and chrome solution are treated with 72 parts of a stock alkali solution hereinafter described, preferably carbonated alkali such as sodium carbonate. These solutions are I mixed before being added to the liquor in which the hides are. When these two solutions are mixed, any precipitation caused by the addition of the sodium carbonate should redissolve. is changed by the sodium carbonate to a dark reddish brown. This new liquor formed by mixing the stock iron and chrome solution and the stock alkali solution is then added to the liquor in the drum in .Whlch the hides have remained, and drumming is continued for a few hours. Then anothermixture is prepared of the stock iron and The color of the liquor chrome solution and the stock alkali soluof borax-in 250 parts of water or other al-' kali solution of equivalent strength is prepared, and enough of this solution s used on the tanned leather so that the amount ofv borax shall be two and one-half per cent. of the weight of the drained leather. The leather is drummed for three quarters of an In case the preliminary tannage" with chrome is not desirable, as this preliminary .tannage is not necessary for certain kinds of leather, the preliminary .tannage can be omitted and the process carried out in all other respects as described.

The certain kinds of leather just referred to in the production of which the.

preliminary tannage withchrome is ,not

desirable and can be omitted, are what are known as the hard leathers, as-for example, sole leather for shoes. The preliminary tannage with chrome produces what are known as soft leathers, which are used for the uppers of shoes, for gloves, &c., and in gen-- eral it may be statcdthatwhen the result desired is a soft leather, the preliminary tannage with chrome should be used, but when the result desired is a hard leather, the preliminary tannage with chrome can be omitted.

The stock iron and chrome solution referred to herein may be prepared as follows: Place 800 parts of sulfate of iron (FeSOJILO) in a spacious vessel, and add lukewarm water enough to cover it. Then add while stirring, 280 parts of commercial The mixture will heat up during this operation. Then add 280 parts of asolution of sodium bichromate (Na Cr O,) containing 33% of chromic acid -(Cr() Enough bichro-mate should be used so that there will be a slight excess of bichromate in order to insure the complete oxidation of the iron. If on testin; it is found that the iron is notfully o-xi- 4 dized, more bichromate should be added.

Cool and let stand. Then add enough water to make the total volume equal to 2000 parts.

Muriatic acid may be used in place of sulfuric acid, and perhaps other acids, but I have so far used sulfuric acid. Potassium bichromate, ammonia bichromate or commercial chromicacid may he used n place of the sodium bichromate.

The reactions in preparing the stock iron and chrome solution may be represented by p The stock alkali solution referred toherein, may be conveniently prepared as follows:

Take 53 parts by'weight of pure carbonateof soda. (Na CO and enough water to make the. combined weight of soda and water 1000 parts. Sodr ash may be used, or washing soda, in place of pure sodium carbonate, using an amount in either case that will contain 53 parts by weightlof pure carbonate of soda. here other alkalis are used, an amount is taken thatwill 'be the chemical equivalent in neutralizing power.

It Wlll of course be understood that any other basic solution of iron containing".

chroinic oxid (Cr. ,O,,) may be used in place of the basic sulfate of iron described, as for I example, the basic chlorid or ni trate' of iron, or a basicsulfate containing substances to prevent precipitation, such substances for example, being sugars.

The amounts of materials given in the forthe amount of leather undergoing treatment.

is one which is familiar to all tanners and need not be discussed. here more at length.

, 'When. the one-bath, preliminary chrome tanning has been employed it is not necessary to add the-stock alkali solution to the first bath of stock iron and chrome solution because the liquor, after adding-the stock iron and chrome solution, is basic and will tan. but after the hides have extracted some of the tanning material it isthen desirable to add basic solutions of iron.

If the hides have been washed, as described in connection with the two-bath, preliminary chrome tanning, this washing will have removed the residual, basic chrome tanning solution and the treatment with the stock iron andchrome solution should commence with the stock iron .and chrome solution which has first been treated with the stock alkali solution as hereinbefo-re de scribed. The remainder of the treatment will then be as described in this specification.

What I claim-is: I

1. The process oftanning hides to produce durable leatherwhich consists in subjectinp; them to the tanning action of both iron and chromium compounds.

2. The process of tanning hides which consists in subjecting the hides to the tan nine action of basic iron salts and basic chromium. compounds.

3. The process of tanning hides which consists in subjecting the hides to the tanning action of chromium compounds and then subjecting them to the combined action of basic chromium compounds and basic iron salts. y 1

4. The process of tanning hides which consists in subjecting them to pickling! solution so that they will absorb acid, then treat ing them to a preliminary chrome'tannage.

- 5 consists in subjecting them to a pickling sothen treating them with basic iron salts and lution and permitting them to drain, then basic chromium compounds in the same solutreating them in an alkali solution to pre-' tion. Vent Washing, out much of the iron, andi 5. The process of tanning hides which finally washing them with lukewarm water.

In witness whereof I hereto afiix my sig- 15 lution sothat they will absorb acid, then nature in presence of two Witnesses.

treating them to a preliminary chrome tan- JOSEPH GUSTAVE STODOLA. nage, then treating them with basic iron Witnesses: I salts and basic chromium compounds in the l CHAS. L. Goss,

10 same solution, removing them from the so- FRANK E. DENNETT. 

